title: Perilipin 1 moves between the fat droplet and the endoplasmic reticulum.
abstract: Perilipin 1, unlike the other perilipins, is thought to be restricted to the fat droplet. We reassessed its cellular distribution using the fat droplet marker CGI-58 in OP9 and 3T3-L1 adipocyte lines and in brown adipose tissue (BAT). As expected, we found perilipin 1 in the fat droplet-enriched floating fraction from centrifuged adipocyte or BAT homogenates. However, about half of perilipin 1 was suspended in the cytosol/infranate or pelleted with cellular membranes. In these fractionations, most of the fat droplet-associated protein CGI-58 was in the floating fraction. In BAT and OP9 adipocytes about a third of perilipin 1 pellets, compared with a much smaller fraction of CGI-58. Co-imaging perilipin 1 and smooth endoplasmic reticulum (ER) markers reveals both ER and fat droplet associated perilipin 1 in OP9 adipocytes. Consistent with these observations, perilipin 1 overexpressed in COS7 cells mostly fractionates with cellular membranes and imaging shows it on the ER. In 3T3-L1 adipocytes almost half of perilipin 1 floats, half is suspended as infranate and small amounts pellet. Finally, driving rapid fat droplet synthesis in OP9 adipocytes increases the intensity of perilipin 1 on fat droplets, while decreasing non-fat droplet immunolabeling. Confirming the morphological findings, fractionation shows perilipin 1 moving from the pelleted to the floated fractions. In conclusion, this study documents an expanded intracellular distribution for perilipin 1 and its movement from ER to fat droplet during lipid synthesis.
authors.affiliation: Center for Human Nutrition; Washington University School of Medicine; St. Louis, MO USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Skinner
authors.forename: Lydia-Ann L S
authors.initials: LA
authors.lastname: Harris
authors.forename: Trevor M
authors.initials: TM
authors.lastname: Shew
authors.forename: Nada A
authors.initials: NA
authors.lastname: Abumrad
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Wolins
keywords: 3T3-L1; CGI-58; OP9; brown fat; diacylglycerol; fractionation; lipid droplets